(Bloomberg) -- Reports of errant drones flouting U.S. regulations including flying too close to passenger airliners and other aircraft surged late last year to an average of four incidents per day, according to Federal Aviation Administration data.

The 1,200 incident reports in 2015 were more than five times the 236 the FAA recorded a year earlier when it first began compiling the data. By the second half of last year, there were an average of four reports per day, according to figures released Friday by the agency.

“We have a number of educational initiatives with our government and industry partners to teach drone operators how to fly safely, including the drone registry we launched last December,” FAA Administrator Michael Huerta said in a press release. “But enforcement goes hand-in-hand with education, and we will take action against anyone who operates irresponsibly to the full extent of the law.”

The incidents grew substantially over the same period a year earlier, even as the FAA began a mandatory registration system for owners of all but the smallest toy drones. There were 93 incidents in January after the registration system for newly purchased drones went into place, compared with 26 in January 2015.

Airline crews

While there were no reported collisions in the latest data and most incidents were sightings with little chance of a mid-air impact, there were numerous instances involving airliners or large aircraft. In the last two weeks of January alone, at least seven airline crews said they spotted drones while flying.

On Jan. 30, ExpressJet Airlines Inc. pilots spotted a white drone within 300 feet (91 meters) while flying at 19,500 feet (5,944 meters) near Atlanta, according to the FAA. ExpressJet is a regional carrier operating flights for American Airlines Group Inc., Delta Air Lines Inc. and United Continental Holdings Inc., according to its website.

Other close calls involving airliners occurred above Miami, Chicago and Salt Lake City, according to FAA.

The FAA requires that drones fly below 400 feet (122 meters) and steer clear of other aircraft. It also says drone operators must stay more than five miles from airports unless they get permission from air-traffic controllers.

The pilot of a hot-air balloon that crashed last summer in Texas, killing himself and 15 sight-seeing passengers, had taken a cocktail of prohibited drugs before liftoff including the opiate pain-killer oxycodone.